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art by opening the menu of the preamplifier/processor or A/V receiver and find the audio menu. This is where the speaker/and or audio functions should be located. Choose the speaker size option and select large or small for the left and right speakers. This choice is based on the size and frequency range of a system’s speakers. If you own full-range or near full-range speakers, choose “large.” If the center and rear channels are smaller, choose “small” for those channels.
2. Next, determine the speakers’ distances from the main seating position. Installers call this the “money seat,” and it’s where the primary user often sits. Input these distances into the receiver or pre/pro. This enables the receiver or pre/pro to calculate the arrival times of sound to the money seat, in order to produce a synchronized soundfield.
3. The next step is to set the system’s crossover frequency. This determines how the system will divide the sound spectrum from low-end bass, to midrange to high frequency or treble. THX’s specification is 80Hz, which means that all frequencies 80Hz and lower will be sent to the LFE (low-frequency effects) channel, which is reproduced by the system’s subwoofer.
4. If possible, use the test tones that are incorporated in the receiver or preamplifier/processor when finishing the sound output leveling process. “For the average user, we do not recommend using an external calibration disc for calibrating audio channels, especially the LFE channel,” Mansfield warns.
“There are a lot of variables in the decoding of a test disc, which could lead to incorrect calibration. For instance, when decoding the LFE test signal from an external disc, the A/V receiver may level-match, and this action is hidden from the user. This risks setting the LFE incorrectly. In addition, today’s technology-rich A/V receivers and DVD/BD players feature numerous modes, filters and EQ settings that may be turned on during the calibration, also throwing off the correct calibration settings.”
A measurement device will be needed, and the most common product used is a sound pressure level (SPL) meter. A lot of custom installers use more advanced devices like real-time analyzers (RTAs) and fast fourier transform (FFT) analyzers for precise measurements.
These products are available through a number of channels like Radio Shack and Guitar Center. There’s an iPod Touch/iPhone app from Studio Six Digital. And Windows Media Center has a built-in app for audio calibration.
The pros use more advanced products from companies like Sencore.
THX guidelines call for each channel’s (or speaker’s) output level to be set at 75dB. Mansfield says this figure is derived from its commercial theater specifications. “The THX Reference Level is 85dB [the same as studio Reference Level]. The 75dB volume level is used for the pink noise generated from THX Certified receivers and pre/pros. [We found the] pink noise at 85dB proved to be too loud for the average consumer. So the pink noise generator is padded down -10 dB, and the receiver accounts for this during calibration. This is why THX recommends the user calibrate with the internal test tone generator.”
After a system’s front, center and surround channels are established, set the output level of the subwoofer.
Adjusting a subwoofer is tricky, due to the science behind sound reproduction and the size of low-frequency soundwaves and how the human ear hears low frequencies.
The simplest way to calibrate a subwoofer is to do it by ear. This may not be the most scientific method, but it avoids the problems that could result from using a device that can’t provide correct measurements. “Many low-cost SPL meters are not as accurate for measuring low frequencies,” notes Mansfield.
“If you are using a more sophisticated SPL meter, make sure you take each LFE measurement for at least 20 seconds, and be sure to take measurements at each seating position, then set the output for the average measurement.”
5. Once the calibration is complete, it’s a good idea to write the settings down and to go through the process again to be sure everything is correct.
Some receivers and pre/pros also offer advanced equalization functions that require some familiarity with acoustics, sound frequencies and sound measurement equipment. These additional functions can deliver an added level of performance to provide smooth and responsive audio that goes beyond the performance of the basic calibration process.
